Many Makers have some Arduino based projects. This beginner's guide on Instructables is a great place to start.
We are also documenting problems (and solutions!) on an "Arduino Debugging" page.
If you are looking for information about certain functions or variables, the Arduino Reference is a great place to start.
Arduino Web IDE
On codebender you can write Arduino code in the browser. Their driver for MacOS X also supports the China clone's USB serial chip. Warning: Codebender has shut down big parts of its service in late 2016.
You can power Arduino boards in various ways, many of which are summarized here.